1. Field of the Invention
This invention relates to muting, or attenuating, speech signals in a compressed voice communication systems in general, and to ADPCM compression in particular, during "fade" periods.
2. Discussion of Related Technology
When wireless communication conditions are severe, or at the limit of usable communications range, bit errors occur rather frequently. Several formats, such as ADPCM, which stands for adaptive delta pulse code modulation, which conforms to a voice compression standard, such as CCITT G.721, can tolerate some bit errors without adversely affecting the quality of speech. But, errors which exceed one in a thousand (10.sup.-3 BER) can cause significant speech degradation.
A system and method are needed to control those unacceptable errors by attenuating, or completely muting, the speech during those significant bit error times. In radio communications, these bit errors often come in bursts, during what is called a "fade", i.e., a temporary loss of radio signal. These fades can last 20 ms or more, and the deleterious effects of those bit errors on speech can be objectionable. Replacing that speech with silence, or attenuating the speech, is an improvement in speech reception quality.